This invention relates to an engine feedback control and more particularly to an improved engine feedback control for a direct injected, internal combustion engine.
In spite of the advantages of two cycle engines over four cycle engines in regard to complexity and high specific output, the environmental concerns are causing reappraisal of the continued use of two cycle engines. Specifically, the overlap between the scavenge port and exhaust port opening and closing gives rise to the possibility that unburned hydrocarbons may pass into the atmosphere through the exhaust port.
It has been thought that the performance of these engines can be improved by utilizing such methodologies as feedback control and/or direct cylinder fuel injection in order to improve their performance and make their continued use more feasible.
With feedback control systems, an engine combustion condition sensor such as an oxygen sensor is positioned in proximity to the combustion chamber or the exhaust system so as to sense the oxygen content of the exhaust gases at the completion of the burning cycle. By determining the amount of oxygen present, it is possible to tell if the engine is running rich or lean. Then, feedback control is possible to maintain the desired fuel/air ratio and, accordingly, improve the exhaust emission control.
Direct cylinder injection also is useful in improving engine performance. With direct cylinder injection, the amount of fuel injected per cycle can be more accurately controlled and this is particularly important with two cycle engines.
However, when two-cycle engines employ fuel injection and the fuel is injected directly into the combustion chamber, the risk of having the fuel pass out of the exhaust port is substantially increased. Therefore, there has been proposed in our copending application entitled "Control for Direct Injected Two-Cycle Engine," Ser. No. 09/188,953, filed Nov. 10, 1998, and assigned to the Assignee hereof, an injection system wherein the timing of fuel injection is controlled so as to be more advanced from the prior art methods so that it occurs before the exhaust port has been totally closed.
The injection timing is initiated, however, at a time so that the first injected fuel will not reach the exhaust port before it closes. This system provides a significantly improved engine performance and emission control.
However, when coupled with feedback controlled, two cycle, direct cylinder injection presents some problems. The reason is that the fuel injector is inherently positioned in closer proximity to the combustion chamber condition sensor than with other types of engines. Thus, the close proximity of the combustion condition sensor in the fuel injector can cause very sensitive fluctuations in the sensor output and unless the control is more accurate, then wide fluctuations in air/fuel ratio and uneven and unsatisfactory running conditions can occur. These problems also exist in four cycle engines.
It is, therefore, a principal object of this invention to provide an improved control strategy for direct injected, feedback controlled, internal combustion engines wherein the fuel injector and the combustion condition sensor are in close proximity to each other.
The problems aforenoted are even more significant in connection with marine application. Because of their high specific outputs and relatively simple construction, two cycle engines are widely utilized in ring propulsion arrangements. However, in connection with such applications it is the normal practice to discharge the exhaust gases to the atmosphere through the body of water in which the watercraft is operating, at least under high speed conditions. In this way, the exhaust gases can be adequately silenced by utilizing the body of water. This is particularly important, due to the extreme compact nature of marine exhaust systems.
However, the discharge of the exhaust gases beneath the level of water gives rise to another problem which aggravates the feedback control. This is that the back pressure can vary rather significantly as the water level changes. This can effect the ability of the exhaust gases to be discharged and can further complicate the accuracy of the feedback control. This is also aggravated by the close proximity of the exhaust condition sensor and the fuel injector.
It is, therefore, a still further object of this invention to provide an improved feedback control system for a marine propulsion engine having direct cylinder injection.